In recent years, thermoplastic elastomers which while having rubber elasticity at normal temperature, do not require a vulcanization step, and similar to thermoplastic resins, are capable of being subjected to forming processing and recycling are frequently used in fields of automotive parts, household electrical appliances, wire covering, medical parts, miscellaneous goods, footwears, and so on. As such thermoplastic elastomers, thermoplastic elastomers containing a hydrogenated block copolymer obtained through hydrogenation of a block copolymer (for example, a styrene-conjugated diene copolymer) having a polymer block composed mainly of an aromatic vinyl compound and a polymer block composed mainly of a conjugated diene compound are known.
The aforementioned hydrogenated block copolymer-containing thermoplastic elastomers can be blended with a rubber softener, a polyolefin resin, such as polypropylene, etc., and so on, and become a material with excellent transparency depending upon a blending ratio, and thus, they are widely utilized for applications bringing out the transparency, such as medical applications, covering materials, packaging materials, toys, etc.
However, a pellet obtained by granulating such a hydrogenated block copolymer-containing thermoplastic elastomer is liable to cause blocking, and there is a case where it becomes difficult to feed the pellet into a blending apparatus or a forming apparatus.
As a method of improving blocking of such a pellet of an elastomer composition, there are known a method of applying an inorganic filler, such as silica, talc, etc., a method of applying a polypropylene fine powder (see PTL 1), a method of impregnating a metallic soap (PTL 2), and so on. However, in pellets of elastomer compositions obtained by these methods, there is a case where in applications requiring especially transparency, the transparency is insufficient, and there was room for improvement.
In addition, the aforementioned hydrogenated block copolymer-containing thermoplastic elastomers are also utilized as a pressure sensitive adhesive upon being blended with a tackifier resin. For example, PTL 3 discloses a method in which in a pressure sensitive adhesive containing a pressure-sensitive adhesive polymer (for example, a styrene-based elastomer) and a tackifier resin, by using an anti-blocking agent having compatibility with the pressure-sensitive adhesive polymer, bleedout of the anti-blocking agent in the pressure sensitive adhesive is prevented from occurring. However, as a result of investigations made by the present inventor and others, it has become clear that because of insufficient transparency and tackiness, there is room for improvement.